CHILDHOOD MYASTHENIA GRAVIS

Objective: The ages at onset of myasthenia gravis (MG) in Japan show two peaks, the highest in the young children around 3 year-old followed by usual peak in young adulthood. This presentation covers the clinical characteristics and treatment of the childhood MG.

Methods: Over 200 childhood onset (younger than 18 year-old) MG cases have been experienced in this clinic. Clinical, electrophysiological and immunological characteristics were evaluated. Results of the treatments were compared in relation to the clinical subtypes.

Results: Sex ratio showed the female predominance (70%) and half of them had onset before 3 year-old. Clinical subtypes were classified to ocular (O), latent generalized (LG) and generalized (G). LG is defined as clinically only ocular symptoms but evoked EMG of extremities revealing generalized involvement. About a third was G, a half was LG and less than 20% was O. Acetylcholine receptor (AChR) antibody revealed either negative or weakly positive in most cases. However, after many years' follow up there have been some cases developing the increase of the titer at around 20 year-old without aggravation of clinical features. HLA of these childhood onset cases, particularly those with onset before 3 years, showed the characteristic class II antibody, i.e. heterozygous combination of DR 9/13 and DQ 6/9. The treatment started with anticholinesterase, and then prednisolone was added in the non-responsive cases. Most cases responded to prednisolone, but relapsed when withdraw was too early. The onset after 12 year-old and particularly G type needed thymectomy. Anti-MUSK antibody revealed to be negative.

Conclusion: Childhood onset MG in Japan is associated with specific HLA antibody. Clinical features are milder than adult onset cases, and ocular involvements are the main feature. However, the pathophysiology is basically similar to adult onset. The immunological mechanism during development may play roles in the characteristic clinical features of childhood onset MG.

Keywords: myasthenia gravis childhood onset, AChR, seronegative, MUSK, prednisolone